In a recent immunohistochemical study we found lack of expression of TGF- beta1, 2, and 3 by neuroblastoma cells, except for well differentiated ganglion cells in ganglioneuroblastomas and in normal ganglia. These data suggested a possible role of TGF-beta in the differentiation of human neuroblastoma. This hypothesis will be further pursued in the following ways: (1) TGF-beta expression and secretion will be studied in neuroblastoma cell lines before and after differentiation with known differentiating agents, such as retinoic acid and TPA. (2) Direct effects of exogenously added TGF-beta in undifferentiated and differentiated neuroblastoma cell cultures will be determined. (3) Blocking antibodies and antisense TGF-beta oligonucleotides will be used to modulate possible actions of TGF-beta on neuroblastoma cells in vitro. Preliminary data have shown induction of TGF-beta1 mRNA in SH-SY5Y neuroblastoma cells following treatment of cultures with TPA or retinoic acid, both of which promoted differentiation. In contrast, another neuroblastoma cell line (IMR-32) which showed minimal morphologic differentiation with the same agents, showed only mild increase in TGF-beta1 mRNA levels. The differences in the TGF-beta expression by neuroblastoma cells before and after differentiation may be the result of induction of surface receptors by the differentiation agents and secondary synthesis of TGF-beta, a phenomenon which will be further pursued by binding studies to determine possible changes of TGF-beta receptors on the surface of neuroblastoma cells before and after treatment with differentiating agents.